The formation of the electrical impulse in the sinus node is necessary to give rise to so-called sinus rhythm. Formation of an impulse in the sinus node is not conspicuous in the superficial ECG itself and can only be detected indirectly from atrial depolarization (P wave).

To better explain rhythm disorders in the region of the sinus node, impulse formation and conduction at the sinus node are represented schematically using a dotted arrow ( in the ECG) and schematically in the diagrams by a dotted line ().